The polymerization of .alpha.-olefins and mixtures thereof at low pressures is known to be promoted by coordination catalysts prepared from mixtures of compounds of (a) transition elements, and (b) organometallic compounds of elements of Groups IA to IIIA of the Periodic Table. Such polymerizations can be carried out in suspension, in solution, in the gas phase, and the like.
Because of favorable process economics, especially with low molecular weight olefins such as ethylene and propylene, it is frequently desirable to carry out olefin polymerization or copolymerization reactions in an inert diluent at a temperature at which the resulting polymer or copolymer does not go into solution; and where the polymer product is recovered without removing the polymerization catalyst. Thus, elaborate steps to remove catalyst from the polymer product are avoided. In order for this more economical method of polymer manufacture to be practical, the polymerization catalyst employed must be capable of producing polymer in high productivities in order to maintain the residual catalyst level in the final polymer at a very low level. Thus, the activity of an olefin polymerization catalyst is one important factor in the continuous search for catalysts useful for the polymerization of .alpha.-olefins. It is also desirable to produce polymer particles which are characterized by high crush or attrition resistant strength, uniformity of size, and a relatively low level of fine particulate matter. Although polymer fluff having relatively high percentages of polymer fines can be handled with plant modifications, the production of polymers in high productivity with low level of fines content is highly desirable so as to avoid the need for such plant modifications.
For certain applications of the polymer, such as for example injection molding, it is desirable that the polymer exhibit easy processibility, characterized by a high melt flow rate. Often the achievement of a high flow rate results in detriment to the mechanical properties of the polymer, e.g., the strength of molded parts made from the polymer is reduced.
It would therefore be desirable to produce a polymer which has a high melt flow rate and yet still retains strength during and after processing.